Ground Excitement

Hi Kathy,

I have not done anything like this but I am curious as to what type of impact it was. Was the masonry structure a brick house? How far away from the stucture was the impact? Was the damage just cracking or something more catastrophic?

Regards,

-John

No the cracking was the major damage. Would have been a treat if the whole thing came down though!

Difficult to scale the soil /sub soil type, underlying rock, foundation and everything else.

But it sounds like a real fun project.

I'd go for dropping a heavy weight as simplest. Or a manageable explosion, say a 12gauge shell fired from some specially designed rig...

Can we all come and play too?

Maybe I'm thinking too small scale....sorry if those ideas are silly...

.

Can I still watch..?

How about one of those specialist food stores?

They have ground spices, ground almonds...maybe Ground Excitement...?

(I bet Verm would sprinkle it on his breakfast cereal ?)

Just being silly now...must be time for the medication...

Hi Del the CAT - Medication = catnip?

I wonder what it will do to a lion?

Hi Kathy - In SA they use a 7 ton weight dropped from a hight of ±5 m to seek out dolomite cavities in the soil.

That might be an acceptable method of producing the required waves.

You might vary the height to calibrate the effect.

"from periodic distances" - I have seen damage to boreholes caused by a time delayed firing of charges in an open cast coal mine. The site was off centre to perpendicular of the firing line. I suppose some of the shock waves met there.

Hi Hendrick,

Kathy says she's going to scale a reenactment but I'm not so sure that's valid here. I think it really depends on what kind of impact occured. If an F16 nose-dived 10 feet from a 100 year old brick structure how ya gonna scale that realistically? In this case though the effect on the structure would be quite obvious.Or suppose a bicycle dropped out of a 747's baggage compartment from 30,000 ft. and landed 50 meters from a concrete military bunker. If a crack was discovered in the bunker could the bike have caused it? Maybe, but I doubt it. Can we scale such a thing?

Suppose a quarter mile wide meteor landed in your backyard. I don't think we'd need to simulate it, do you? Hendrick? Hey Hendrick! Can you hear me?

Hi Johnx2

A test with a dropping weight might be used to establish the trend of the underlying geology.

All depending on the impact the test should begin at a low height. say 1/2 a meter or less. The reading on the sensors should be taken and tabulated.

The height should then be increased step by step but must be stopped before further damage.

With the figures the behavior of the vicinity can be calibrated and eventually extrapolated to simulate the impact that allegedly caused the damage.

I hope that was what Kathy had in mind.

MY first thought was to suggest a model but I don't think that would have been sufficient proof in a court of law.

Good answer and I agree. I was just teasing you earlier.

John²

Dear Kathy, I think too (as Mr Hendrik said) that a weight dropping coul do. All this depending upon the scale ot the impact you want to simulate. I think that not only distance and mass of the weight but the shape of the same should be important to achieve the desired effects. Am I right?... Best regards, Abel. PD: dear Kitty... forget about medicines. A daily bit of salt is highly advisable under all circumstances. ; )

Might I suggest looking into the technology used in Seismic production of the oil fields and used in geology. There are many simulation programs available. You should be able to modify the parameters to meet your needs in a simulation(s) to recreate the results that you are looking for. There is also the Colorado School of Mines they might have better information as to seismic events on various substrates. The other possibility is to reenact the event using the the "Thumper" used in seismic mapping it would be useful in varying the distances and the impact simulation, as to magnitude. It would be the most realistic reenactment method with out actually recreating the event via explosives or another crash. And it would provide a graphic record of the events in the actual build up to the climatic point of collapse of the structure, thus providing a traceable graphic record to prove or disprove your required results.

If you contact the US Bureau of Mines, you will find that they have conducted many, many analyses of vibration effects on various structures initiated by blasting events. I was once in the contracting business and used dynamic compaction as a tool for compacting loose soils to depths of 25' or more. This process involved dropping an 11-ton weight with about a 20 square foot footprint from heights up to 50', repeatedly (usually 3-5 times at each node of a 10' square pattern). The resulting vibration was very low frequency (8-15 hz), and caused peak particle velocities (ppv) of 0.5 to 1.5 inches per second per second at distances of 150' from the impact. The vibration level is a function of the soil type, the distance of the measurement point from the impact, and the groundwater level. High groundwater levels tend to increase the acceleration or prevent it from decay over longer distances.

USBM experiments conclude that ppv values of 2.0 ips at frequencies above 15 hz can cause very minor cracking in cement plaster. In my experience, we often induced vibrations of 5+ ips at frequencies in the 8-15 hz range in the soil adjacent to masonry structures without observing any new cracking in the masonry. The USBM threshhold curve for minor damage follows a level of 0.5 ips at the lower frequencies up to 12 hz and then steps up to 2.0 ips at about 20 hz.

Using seismic simulators works for general observations, but if the building was built on a rock ledge in the sub strata (think see saw) wouldn't you need to test your theory directly at the impact site and register your results at the perimeter of the building? I've seen buildings shift an entire floor from a coal mine collapse and you'd swear it was actually built that way. If it wasn't for the exposed interior on the top floor.

Take a look at this abstract to get an idea of complexity of your project. I would recommend you call Mr. Siskind. I have found him to be helpful, although is has been several years since I last consulted with him. It is likely that he's even tried something similar to what you propose - he's done a ton of research.

http://www.isee.org/tis/Proceed/Research/98Resrch/9801r.pdf

This will link you to the following paper:

GROUND VIBRATION EFFECTS ON STRUCTURES

David E. Siskind

DESA, D. E. Siskind and Associates, LLC

I believe you can contact MR. Siskind at:

D.E. Siskind & Associates
5812 Thomas Circle
Minneapolis
MN
USA 55410
612-929-4498
612-929-4498